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Xbox 360 - Quake 4 cheats

Get all:
During gameplay press the "back" button on the controller to display the 
objectives window, after quickly press:
Up, Up, Down, Down, Left, Right, Left, Right, B, A. 

Full health:
During gameplay press the "back" button on the controller to display the 
objectives window, after quickly press:
B, A, B, A, Up, Up, Down, X. 

Full ammo + refill all weapons:
During gameplay press the "back" button on the controller to display the 
objectives window, after quickly press: B, A, X, Y, Left, Right, Left.

Never die:
During gameplay press the "back" button on the controller to display the 
objectives window, after quickly press:
Down, Up, Down, Down, Up, Right, Left, Right, Y, X, X, A. 
Your health will never drop to zero. Falling still kills you.

Note: 
Do not use cheat codes, If you want to get the gamerscore achievements.